The present invention relates to a new corrosion- and wear-resistant high temperature composite material based on an alloy of the MCrAlY type as the matrix metal with platinum and/or rhodium as alloy elements in amounts of 5 to 15 wt. %, a process for the preparation of this high temperature composite material and its use.
In many modern industrial plants, such as e.g. in energy production, waste combustion or coal gasification, components of the plant must be resistant towards corrosion at high temperatures and wear or be substantially protected from these circumstances by suitable coatings.
The use of materials with the general designation MCrAl(Y) alloys (the yttrium component being in some instances, optional) wherein M represents a metal from the group comprising iron, cobalt and nickel or combinations of these elements, is known from the field of gas turbine construction, in particular in aircraft engines. Materials of this type are described in U.S. Pat. Nos. 3,874,901; 3,928,026; 3,542,530; and 3,754,903. Further development of MCrAlY alloys with the aim of increasing the resistance to corrosion has led to alloy types containing noble metals. U.S. Pat. No. 3,918,139 describes an MCrAlY alloy containing 3 to 12 wt. % platinum or rhodium. Platinum-containing coating alloys based on NiCrAl have in the past exhibited an outstanding resistance to corrosion in many cases.
According to U.S. Pat. Nos. 3,879,831 and 4,124,737 it is possible to improve the wear properties of MCrAlY materials by adding inter alia, mechanically resistant substances, such as oxides and nitrides, to the base alloys. It is moreover known from U.S. Pat. No. 4,275,124 that the wear properties of MCrAlY alloys can be increased by carbides formed in situ or by alloyed carbides.
Chromium carbide, Cr.sub.3 C.sub.2, is mentioned as an additive in U.S. Pat. No. 4,275,090. The addition of TaC to Ni--Cr and Co--Cr materials is also indeed known from U.S. Pat. Nos. 4,117,179 and 4,124,137, but the influence of tantalum on the oxidation corrosion properties is predominantly reported as being negative.
The carbides included in the MCrAlY matrix react to a greater or lesser degree in the matrix under the operating temperatures which occur, because of the physical and chemical properties of this composite system. The rate of reaction increases as the temperature increases, and carbides of the 6th sub-group (e.g. Cr.sub.3 C.sub.2) are degraded faster at the same temperature than those of the 4th sub-group (e.g. TiC, NbC). Since the efficiency of many plants which operate at high temperatures can be further increased by increasing the temperature, however, materials which are stable at high temperatures and resistant to corrosion and wear are required.
The object of the invention is therefore to improve the stability to high temperatures of the composite materials of an MCrAlY matrix and mechanically resistant substances in order to overcome the disadvantages of the known material combinations. Heat-stable corrosion- and wear-resistant alloys which can be used at temperatures of 600.degree. to 1,100.degree. C. are thus accordingly to be provided.